Heat exchanger

ABSTRACT

A heat exchanger has tubes defining first fluid passages through which a first fluid flows therein, an inlet part and an outlet part. Each tube has a first main wall and a second main wall. At least one of the first main wall and the second main wall has a projection projecting outside of the tube along a peripheral end and a first recess and a second recess recessed from the projection. The tubes are stacked such that the first and second main walls are opposed to each other and spaces are provided between the adjacent tubes by the projections. The spaces define second fluid passages through which a second fluid flows. The inlet part is in communication with the second fluid passages through the first recesses and the outlet part is in communication with the second fluid passages through the second recesses.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2006-27277filed on Feb. 3, 2006 and No. 2007-012991 filed on Jan. 23, 2007, thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger, which is for exampleused in an exhaust gas recirculation system (EGR) for performing heatexchange between an exhaust gas and a cooling water.

BACKGROUND OF THE INVENTION

Japanese Unexamined Patent Publication No. 2003-106790 (U.S. Pat. No.6,595,274 B2) discloses an exhaust gas heat exchanger, which is forexample used in an exhaust gas recirculation system. The exhaust gasheat exchanger performs heat exchange between a part of an exhaust gasthat is discharged from an engine and returned to an air intake side ofthe engine and a cooling water, thereby to cool the exhaust gas.

In the exhaust gas heat exchanger, stacked tubes are housed in a tank,and bonnets are coupled to longitudinal ends of the tank. Also, coreplates are provided at the longitudinal ends of the tank so as toseparate the space inside of the tank from spaces of the bonnets. Thelongitudinal ends of the tubes are inserted to holes of the core plates.Further, a cooling water inlet pipe and a cooling water outlet pipe arecoupled to the tank to make communication with the space defined in thetank.

The cooling water entering from the cooling water inlet pipe flowsthrough spaces (water passages) defined outside of the tubes in the tankand flows out of the tank from the cooling water outlet pipe. On theother hand, the exhaust gas is introduced into gas passages definedinside of the tubes from one of the bonnets. The exhaust gas iscollected in the other bonnet and discharged to be returned to theengine. Thus, the exhaust gas is cooled by the cooling water whileflowing through the tubes.

In the exhaust gas heat exchanger, the core plates are provided tosupport the tubes such that the spaces for the water passages areprovided between the adjacent tubes. Namely, the core plates will notcontribute to heat exchanging performance. In manufacturing the exhaustgas heat exchanger, it is necessary to insert the longitudinal ends ofthe tubes into the holes of the core plates. Thus, steps increase in themanufacturing process, resulting in increase in manufacturing costs.

SUMMARY OF THE INVENTION

The present invention is made in view of the foregoing matter, and it isan object of the present invention to provide a heat exchanger having astructure capable of providing spaces between adjacent tubes withoutusing a core plate.

According to an aspect of the present invention, a heat exchanger has aplurality of tubes, an inlet part and an outlet part. Each of the tubesdefines a first fluid passage therein through which a first fluid flows.Each tube has a first main wall and a second main wall, and at least oneof the first main wall and the second main wall has a projectionprojecting outside of the tube and along its peripheral end. A firstrecess and a second recess are formed on the projection at predeterminedpositions. The tubes are stacked such that the first main walls and thesecond main walls are opposed to each other and spaces are providedbetween the adjacent tubes by the projections. The spaces define secondfluid passages through which a second fluid flows. Also, first openingsare defined by the first recesses and second openings are defined by thesecond recesses. The inlet part is disposed in communication with thefirst openings for introducing the second fluid into the second fluidpassages. The outlet part is disposed in communication with the secondopenings for discharging the second fluid from the second fluidpassages.

In this construction, the spaces for the second fluid passages areprovided between the adjacent tubes by the projections, without usingcore plates. Therefore, steps of manufacturing the heat exchangerreduces.

The inlet part is for example constructed of an inlet portion forintroducing the second fluid and a distributing portion for distributingthe second fluid flowing from the inlet portion into the second fluidpassages. The outlet part is for example constructed of a collectingportion for collecting the second fluid having passed through the secondfluid passages therein and an outlet portion for discharging the secondfluid from the collecting portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description made withreference to the accompanying drawings, in which like parts aredesignated by like reference numbers and in which:

FIG. 1 is a schematic plan view of an EGR gas cooler according to afirst embodiment of the present invention;

FIG. 2 is a schematic side view of the EGR gas cooler according to thefirst embodiment;

FIG. 3 is a schematic side view of the EGR gas cooler when viewed alongan arrow Al in FIG. 2;

FIG. 4 is an exploded perspective view of the EGR gas cooler accordingto the first embodiment;

FIG. 5A is a top view of a tube of the EGR gas cooler according to thefirst embodiment;

FIG. 5B is a side view of the tube according to the first embodiment;

FIG. 5C is a bottom view of the tube according to the first embodiment;

FIG. 6 is a schematic cross-sectional view of a part of the tube as anexample according to the first embodiment;

FIG. 7 is a schematic cross-sectional view of a part of the tube asanother example according to the first embodiment;

FIG. 8 is a schematic side view of a stack of tubes of the EGR gascooler according to the first embodiment;

FIG. 9 is a schematic cross-sectional view of the EGR gas cooler takenalong a line IX-IX in FIG. 1;

FIG. 10 is a cross-sectional view of the EGR gas cooler taken along aline X-X in FIG. 2;

FIG. 11 is a schematic cross-sectional view of a joining portion betweena first tank member and a second tank member of the EGR gas cooleraccording to the first embodiment;

FIG. 12 is a schematic cross-sectional view of the EGR gas cooler takenalong a line XII-XII in FIG. 9; and

FIG. 13 is a schematic cross-sectional view of an EGR gas cooleraccording to a second embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENT

A first embodiment will be described with reference to FIGS. 1 to 12. Aheat exchanger shown in FIG. 1 is for example used as an EGR gas coolerfor an exhaust gas recirculation system (EGR) of a diesel engine.

As shown in FIGS. 1 to 4, an EGR gas cooler 100 performs heat exchangebetween an exhaust gas (first fluid) to be returned to an engine of avehicle and an engine cooling water (second fluid), thereby cooling theexhaust gas. In the drawings, arrows CW denote flows of the coolingwater, and arrows EG denote flows of the exhaust gas.

Components of the EGR gas cooler 100 are made of materials, such asstainless, having sufficient strength and sufficient resistance tocorrosion. The respective components are joined by such as brazing orwelding.

The EGR gas cooler 100 has a stack of tubes 110, a water tank 130, afirst gas tank 151, and a second gas tank 152. As shown in FIGS. 5A to9, each tube 110 has a substantially flat tubular shape and defines agas passage (first fluid passage) 114 therein through which the exhaustgas flows. The tube 110 has a substantially rectangular-shapedcross-section.

For example, each tube 110 is constructed of a first tube plate (firsttube member) 110 a and a second tube plate (second tube member) 110 b.Each of the first and second tube plates 110 a, 110 b is shaped from aflat plate member such as by pressing or rolling to have a substantiallyU-shaped cross-section. Specifically, the tube plate 110 a, 110 b has amain wall and side walls on opposite sides of the main wall.

As shown in FIG. 6, the first and second tube plates 110 a, 110 b arejoined such that the respective side walls partly overlap with eachother. FIG. 6 shows an example in which the side walls overlap at asubstantially middle portion of a side of the tube 110. FIG. 7 showsanother example in which the side walls overlap at a position close tothe main wall of the second tube plate 110 b. The main wall of each tubeplate 110 a, 110 b provides a tube main wall (opposed wall) 111. Thejoined side walls of the tube plate 110 a, 110 b provide tube side walls118.

The tube 110 has an inner fin 120 therein. The inner fin 120 is forexample a corrugated fin and formed from a thin plate member bypressing. For example, the inner fin 120 is interposed between the firstand second tube plates 110 a, 110 b and joined such as by brazing. Assuch, the inner fin 120 is joined to inner surfaces of the tube mainwalls 111.

The tubes 110 are stacked such that the tube main walls 111 are opposedto each other, as shown in FIGS. 4, 8 and 9. The gas passages 114 areformed within the tubes 110. On the other hand, water passages (secondfluid passages) 115 through which the cooling water flows are providedby spaces defined between the adjacent tubes 110. The main walls 111 ofthe outermost tubes 110, which are disposed on outermost layers of thestack of the tubes 110, provide outermost tube walls 111 a.

Each of the tube 110 has projections 112 and recesses 113 on its bothmain walls 111, as shown in FIGS. 5A to 5C. Here, all tubes 110 have thesame structure. Thus, the outermost tubes 110 also have the projections112 and the recesses 113 on the outermost tube walls 111 a, as shown inFIG. 4.

The projection 112 projects outwardly from the tube main wall 111. Theprojection 112 is for example formed by pressing. The projection 112 isformed along a peripheral end of the tube main wall 111 like acontinuous dam.

The recesses 113 are recessed from a top end of the projection 112toward the tube main wall 111. Each recess 113 has a predeterminedlength in a longitudinal direction of the tube main wall 111. Thedimension of the recess 113 is for example equal to the dimension(height) of the projection 112 in a direction perpendicular to the tubemain wall 111. In other words, the projection 112 is not formed at apart corresponding to the recess 113.

Here, two recesses 113 are formed on each tube main wall 111. Also, therecesses 113 are located on diagonal positions and along longitudinalsides of the tube main wall 111.

Further, the tube 110 has first raised portions 116 on both tube mainwalls 111 thereof. The first raised portions 116 are arranged atpredetermined intervals over the tube main wall 111. Each raised portion116 projects outwardly from the tube main wall 111 in a form of tube andhas the same dimension (height) as the projection 112 in a directionperpendicular to the tube main wall 111.

The tube 110 further has second raised portions 117 on both tube mainwalls 111 thereof as flow-adjusting portions for adjusting or arrangingthe flow of the cooling water. Each second raised portion 117 is locatedadjacent to one of the recesses 113 (left recess in FIGS. 5A and 5C,hereafter, referred to as a first recess 113), which is located upstreamof the other recess 113 with respect to the flow of the cooling water.

The second raised portion 117 extends parallel to a short side of thetube main wall 111, i.e., extends perpendicular to a longitudinaldirection of the tube 110. The second raised portion 117 has the sameheight as the projection 112. Further, the second raised portion 117 islocated closer to a first end 112 a of a first portion of the projection112 than a second end 112 b of the projection 112 with respect to thelongitudinal direction of the tube main wall 111. The first portionextends along the longitudinal side of the tube main wall 111, and thesecond portion extends along the short side of the tube main wall 111.

Furthermore, the second raised portion 117 is located such that adistance between its first end (upstream end) 117 a and the longitudinalside of the tube main wall 111 is smaller than a distance between itssecond end (downstream end) 117 b and the opposite longitudinal side ofthe tube main wall 111, with respect to a direction perpendicular to thelongitudinal direction of the tube 110.

As shown in FIG. 8, the tubes 110 having the above structure are stackedsuch that the respective projections 112 are opposed and in contact witheach other. As such, the tubes 110 are joined to each other at theprojections 112. In this case, the first raised portions 116 and thesecond raised portion 117 have the same height as the projection 112.Thus, the adjacent tubes 110 are also in contact with and are joined atthe first raised portions 116 and the second raised portion 117.Further, the inner fins 120 are joined to the inner surfaces of thetubes 110. Accordingly, the strength of the stack of the tubes 110improves.

In the stack of the tubes 110, spaces are provided between the adjacenttubes since the projections 112 are formed on the tube main walls 111.Each space is surrounded by the projections 112. As such, the coolingwater passage 115 is defined by this space except for the first raisedportions 116 and the second raised portions 117, as shown in FIGS. 9 and12.

Further, openings 113 a are provided by the recesses 113 of the adjacenttubes 110. Here, the openings 113 a provided by the first recesses 113,which are adjacent to the second raised portions 117, define inletopening 113 a for introducing the cooling water into the cooling waterpassages 115. The openings 113 b provided by the second recesses 113(right recesses 113 in FIG. 5B), which are further from the secondraised portion 117, define outlet openings 113 b for discharging thecooling water from the cooling water passages 115.

The water tank 130 includes a first tank member 130 a and a second tankmember 130 b, which are arranged in the longitudinal direction of thetubes 110. The first tank member 130 a is disposed adjacent to the inletopenings 113 a of the stack of the tubes 110, and the second tank member130 b is disposed adjacent to the outlet openings 113 b of the stack ofthe tubes 110.

Each of the first and second tank members 130 a, 130 b has asubstantially U-shape and includes outer walls 131 and a connecting wall132 between the outer walls 131. The outer walls 131 are parallel toeach other. The first and second tank members 130 a, 130 b are formedfrom plate members by bending, for example.

The first and second tank members 130 a, 130 b are coupled to the stackof the tubes 110 so as to substantially surround the stack of the tubes110. Thus, the outer walls 131 are opposed to the outermost tube walls111 a and the connecting walls 132 are opposed to the tube side walls118.

In this case, since the inlet openings 113 a and the outlet openings 113b are located on diagonal positions of the stack of the tubes 110, thefirst and second tank members 130 a, 130 b are coupled from oppositesides of the stack of the tubes 110. Specifically, the connectingportion 132 of the first tank member 130 a are opposed to the inletopenings 113 a, and the connecting portion 132 of the second tank member130 b are opposed to the outlet openings 113 b.

Further, as shown in FIG. 11, the first and second tank members 130 a,130 b are engaged with each other at ends thereof such that the outerwalls 131 thereof share a plane. Thus, the first and second tank members130 a, 130 b are engaged at a substantially middle position of the stackof the tubes 110 in the longitudinal direction of the tubes 110. Forexample, the ends of the first and second tank members 130 a, 130 boverlap with each other.

Although the first and second tank members 130 a, 130 b are coupled tothe stack of the tubes 110 in opposite directions, these have the sameshape. Thus, the specific shape of the first and second tank members 130a, 130 b is described hereafter about the first tank member 130 a as anexample.

As shown in FIGS. 1, 2 and 10, a peripheral end of each outer wall 131is in contact with and joined to the projection 112 of the outermosttube wall 111 a. A main portion of each outer wall 131, other than theperipheral end, is raised from the peripheral end in an outwarddirection of the U-shaped tank member 130 a. Further, first recesses135, a second recess 136, and reinforcement ribs 137 are formed on theraised main portion of each outer wall 131.

The first recesses 135 are recessed from the raised main portion so asto be in contact with and joined to the first raised portions 116 of theoutermost tube wall 111 a. The second recess 136 is recessed from theraised main portion so as to be in contact with and joined to the secondraised portion 117 of the outermost tube wall 111 a, as theflow-adjusting portion. The reinforcement ribs 137 are located betweenthe first recesses 135 and project from the raised main wall, as shownin FIG. 2.

As shown in FIGS. 9 and 10, a space is provided between one outer wall131 and the outermost tube wall 111 a. The space is surrounded by theperipheral end of the outer wall 131 and the projection 112 of theoutermost tube wall 111 a. Thus, similar to the cooling water passages115, an end water passage 115 a is defined by this space except for thefirst raised portions 116, the first recesses 135 and the second raisedportion 117 and the second recess 136.

Further, as shown in FIG. 8, an end opening 113 c is formed between theouter wall 131 and the first recess 113 of the outermost tube 110 forintroducing the cooling water into the end water passage 115 a.Likewise, the end opening 113 c is formed between the outer wall 131 andthe second recess 113 of the outermost tube 110 for discharging thecooling water from the end water passage 115 a.

The connecting wall 132 of the first tank member 130 a is in contactwith and joined to the side walls 118 on which the inlet openings 113 a,113 c are formed. Likewise, the connecting wall 132 of the second tankmember 130 b is in contact with and joined to the side walls 118 onwhich the outlet openings 113 a, 113 c are formed.

The first tank member 130 a is also formed with a bulge 133. The bulge133 expands in an outward direction of the first tank member 130 a andextends over the outer walls 131 and the connecting wall 132. In theconnecting wall 132, the bulge 133 is opposed to the inlet openings 131a, 131 c so as to cover or encases the inlet openings 131 a, 131 c, anda clearance 133 a is defined between an inner surface of the bulge 133and the inlet openings 113 a, 113 c of the tubes 110, as shown in FIG.12. The clearance 133 a is in communication with the water passages 115,115 a thorough the inlet openings 113 a, 113 c. Further, the end waterpassages 115 a are partly expanded by the bulge 133 formed on the outerwalls 131, as shown in FIG. 9.

As shown in FIGS. 4 and 12, a pipe hole 134 is formed on the bulge 133.A water inlet pipe (pipe member) 141 is coupled to the inlet hole 134.Thus, the water passages 115, 115 a are in communication with an outsideof the EGR gas cooler 100 through the inlet openings 113 a, 113 c, theclearance 133 a, the pipe hole 134 and the water inlet pipe 141. Thus,an inlet part is provided by the water inlet pipe 141 and the bulge 133(clearance 133 a) of the first tank member 130 a. The water inlet pipe141 corresponds to an inlet portion for introducing the cooling waterinto the clearance 133 a of the bulge 133, and the bulge 133 (clearance133 a) corresponds to a distribution portion for distributing thecooling water into the water passages 115, 115 a.

Likewise, a water outlet pipe (pipe member) 142 is coupled to the bulge133 of the second tank member 130 b. The water passages 115, 115 a arealso in communication with the outside through the outlet openings 113b, 113 c, the clearance 113 a, the pipe hole 134 and the water outletpipe 142. Thus, an outlet part is provided by the water outlet pipe 142and the bulge 133 (clearance 133 a) of the second tank member 130 b. Thebulge 133 a (clearance 133 a) corresponds to a collecting portion forcollecting the cooling water discharged from the water passages 115, 115a and the water outlet pipe 142 corresponds to an outlet portion fordischarging the cooling water from the collecting portion to theoutside.

The first gas tank 151 and the second gas tank 152 are coupled to thelongitudinal end of the stack of the tubes 110. For example, the firstgas tank 151 is coupled to the first end adjacent to the inlet part, andthe second gas tank 152 is coupled to the second end adjacent to theoutlet part.

The first gas tank 151 has a cup shape for defining a tank spacetherein. The first gas tank 151 is coupled such that its end defining anopening is in contact with and joined to the peripheral portions of thefirst ends of the stacked tubes 110 and the end of the first tank member130 a. Thus, the tank space of the first gas tank 151 is incommunication with the gas passages 114 defined inside of the tubes 110.

Further, a gas inlet pipe 151 a is coupled to a side wall of the firstgas tank 151 to be in communication with the tank space. For example,the gas inlet pipe 151 a and the water inlet pipe 141 are disposed onthe same side of the EGR gas cooler 100. The gas inlet pipe 151 a has aflange 151 b to be coupled to the exhaust gas recirculation system. Assuch, the gas passages 141 are in communication with the exhaust gasrecirculation system through the first gas tank 151 and the gas inletpipe 151 a.

The second gas tank 152 has the shape similar to the first gas tank 151.The second gas tank 152 is coupled such that its end defining an openingis in contact with and joined to the peripheral portions of the secondends of the stacked tubes 110 and the end of the second tank member 130b. Thus, a tank space defined in the second gas tank 152 is incommunication with the gas passages 114.

Further, a gas outlet pipe 152 a is coupled to a side wall of the secondgas tank 152. For example, the gas outlet pipe 152 a is disposed on thesame side as the gas inlet pipe 151 a and the water inlet pipe 141. Thegas outlet pipe 152 a has a flange 152 b at its end. Thus, the exhaustgas having passed through the gas passages 114 is discharged from theEGR gas cooler 100 through the second gas tank 152 and the gas outletpipe 152 a.

In this EGR gas cooler 100, as shown by the arrows EG in FIG. 1, a partof the exhaust gas discharged from the engine flows in the gas passages114 from the inlet gas pipe 151 a, the first gas tank 151. The exhaustgas having passed through the gas passages 114 is discharged through thesecond gas tank 152 and the gas outlet pipe 152 a and returned to theengine.

On the other hand, as shown by the arrows CW in FIG. 1, the enginecooling water flows in the water passages 115, 115 a from the inlet partprovided by the water inlet pipe 141, the clearance 133 a and the inletopenings 113 a, 113 c. The cooling water having passed through the waterpassages 115, 115 a are discharged from the inlet part provided by theoutlet openings 113 b, 113 c, the clearance 133 a, and the water outletpipe 142.

As such, the heat exchange is performed between the exhaust gas flowingthrough the gas passages 114 and the cooling water flowing through thewater passages 115, 115 a. As a result, the exhaust gas is cooled.

In a general heat exchanger, tube holes are formed on core plates atpredetermined intervals and ends of the tubes are inserted to tube holesof the core plates. That is, the tubes are held with predeterminedspaces by the core plates so as to provide passages between the adjacenttubes.

In the EGR gas cooler 100, the projections 112 and the recesses 113 areformed on the tube main walls 111. Thus, the water passages 115 aredefined by the spaces provided between the tube main walls 111 of theadjacent tubes 110, and the inlet and outlet openings 113 a, 113 b, 113c are provided by the recesses 113.

Accordingly, the gas passages 114 and the water passages 115 areseparated without requiring core plates. That is, the water passages 115are provided without using the core plates. Also, since the core platesare not required, a step of inserting the ends of the tubes into theholes of the core plates is not necessary in manufacturing the EGR gascooler 100. Therefore, manufacturing cots of the EGR gas cooler 100reduce.

In this embodiment, the dimension of the recesses 113 is equal to theheight of the projections 112. Therefore, the size of the inlet andoutlet openings 113 a, 113 b is increased. Thus, resistance of thecooling water to flow in and out of the water passages 115 reduces.

Also, the inlet openings 113 a and the outlet openings 113 b are locatedon diagonal positions of the tube main walls 111. Therefore, a regionwhere the cooling water easily stagnate is reduced. Namely, it is lesslikely that the cooling water will stagnate in the water passage 115.Accordingly, heat exchange efficiency improves.

Further, the second raised portions 117 are formed on the tube mainwalls 111 as the flow-adjusting portions. Therefore, the cooling waterentering from the inlet openings 113 a, 113 c can be directed toward thesecond ends 117 b of the second raised portions 117 to flow furtherinside of the tubes 110, as shown by a dashed arrow CW1 in FIG. 5A. Assuch, the cooling water can be substantially uniformly introduced overthe water passages 115. Namely, the heat exchange is performed byeffectively using the tube main walls 111. Accordingly, the heatexchange efficiency improves.

In a case that the cooling water stagnates in the water passage 115 at aposition corresponding to a portion where the high temperature exhaustgas flows, heat exchange is excessively performed, resulting in boilingof the cooling water. In the embodiment, however, the second raisedportion 117 is formed at an upstream side of each tube main wall 111with respect to the flow of the exhaust gas. Therefore, it is lesslikely that the cooling water will boil due to the excess heat exchange.

In the embodiment, each tube 110 is constructed by joining the first andsecond tube plates 110 a, 110 b. The first and second tube plates 110 a,110 b are formed such as by bending, pressing, rolling and the like.Therefore, the tubes 110 are produced easily and with reduced costs, ascompared with a case in which a tube is formed by shaping a cylindricaltube member into a flat tubular shape.

In addition, since the inner fins 120 are provided in the gas passages114 of the tubes 110, turbulence effect is provided to the flow of theexhaust gas. As such, the heat exchange efficiency further improves.

The projections 112 and the recesses 113 are also formed on theoutermost tube walls 111 a of the outermost tubes 110, and the outerwalls 131 of the tank members 130 a, 130 b are joined to the projections112 of the outermost tube walls 111 a. Therefore, the end water passages115 a with the end inlet and outlet openings 113 c are formed betweenthe outermost tube walls 111 a and the outer walls 131. As such, sincethe heat exchange area increases, the heat exchange efficiency improves.

In each tank members 130 a, 130 b, the outer walls 131 are connectedthrough the connecting wall 132. Namely, the outer walls 131 areintegrally formed into the tank member 130 a, 130 b. Therefore, the tankmember 130 a, 130 b is easily coupled to the stack of the tubes 110 byinserting the stack of the tubes 110 into the space defined between theouter walls 131.

The connecting walls 132 of the first and second tank members 130 a, 130b are opposed to and joined to the side walls 118 of the tubes 110. Thebulges 133 are formed on the connecting walls 132 at positionscorresponding to the inlet and outlet openings 113 a, 113 b, 113 c suchthat the clearances 133 a are provided between the inner surfaces of thebulges 133 and the inlet and outlet openings 113 a, 113 b, 113 c.Further, the water inlet pipe 141 and the water outlet pipe 142 arecoupled to the pipe holes 134 formed on the bulges 133.

As such, the inlet part and the outlet part are provided by the bulges133 and the water inlet and outlet pipes 141, 142. Namely, The inletpart and the outlet part are formed with simple structure. With thisconfiguration, expansion loss or reduction loss while the cooling waterflows into and out of the water passages 115, 115 a reduces. That is,because pressure loss of the flow of the cooling water reduces, the heatexchange efficiency improves.

Second Embodiment

A second embodiment will be described with reference to FIG. 13. In thesecond embodiment, a EGR gas cooler 100A has bypass tubes 110A and apartition wall 160 in addition to the structure of the EGR gas cooler100 of the first embodiment. In FIG. 13, the water inlet part isexemplary shown because a water inlet part and a water outlet part havethe similar structure.

The bypass tubes 110A are stacked on one side (lower side in FIG. 13) ofthe stack of the tubes 110. The bypass tubes 110A define the gaspassages 114 through which the exhaust gas flows, similar to the tubes110. The partition wall 160 is interposed between the tube 110 and thebypass tube 110A. The partition wall 160 is for example made ofstainless and has a rectangular shape. The stack of the tubes 110,partition wall 160 and bypass tubes 110A is disposed in the water tank130.

Similar to the first embodiment, the water tank 130 includes the firsttank member 130 a and the second tank member 130 b. The stack of thetubes 110, partition wall 160 and the bypass tubes 110A are locatedbetween the outer walls 131 of the tank members 130 a, 130 b.

An end tube 110 s, which is one of the tubes 110 and is opposed to thepartition wall 160, has a projection 112, similar to the other tubes110. Thus, the end tube 110 s is in contact with and joined to thepartition wall 160 at the projection 112. An end water passage 115 b isformed between the tube main wall 111 of the end tube 110 s and thepartition wall 160.

Further, the recesses 113 are formed on the end tube 110 s. Thus, aninlet opening 113 d is provided between the recess 113 of the end tube110 s and the partition wall 160. The end water passage 115 b is incommunication with the clearance 133 a through the inlet opening 113 d.

In the example of FIG. 13, the EGR gas cooler 100A has two bypass tubes110A. Similar to the tubes 110, each of the bypass tubes 110A isconstructed of a first tube plate and a second tube plate. The bypasstubes 110A define the gas passages 114 therein through which the exhaustgas flows. Although not illustrated, reinforcement plates are interposedbetween the first and second tube plates and joined to inner walls ofthe first and second tube plates. Each reinforcement plate has a crankshape in its cross-section with a pitch greater than that of the innerfin 120 of the first embodiment.

The bypass tubes 110A are formed with projections 112A, similar to theprojections 112 of the tubes 110. Thus, the bypass tubes 110A arestacked such that the projections 112A are opposed to and joined to eachother. Further, spaces are provided between the adjacent bypass tubes110A as thermal insulation spaces.

A first end bypass tube 110A1, which is one of the bypass tubes 110A andis opposed to the partition wall 160, is joined to the partition wall160 at the projection 112A thereof. Thus, the thermal insulation space115 c is also provided between the partition wall 160 and the tube mainwall of the first end bypass tube 110A1.

A second end bypass tube 110A2, which is one of the bypass tubes 110Aand is opposed to the outer wall 131, is joined to the outer wall 131through the projection 112A thereof. Thus, the thermal insulation space115 c is also provided between the tube main wall of the second endbypass tube 110A2 and the outer wall 131.

A portion of the partition wall 160, which corresponds to the bulge 133,extends across the clearance 113 a. The end of the portion of thepartition wall 160 is in contact with and joined to an inner wall of thebulge 133. Therefore, the thermal insulation spaces 115 c definedoutside of the bypass tubes 110A are separated from the water passages115, 115 a, 115 b defined outside of the tubes 110 and the clearance 113a by the partition wall 160. As such, the cooling water is not allowedto enter the thermal insulation spaces 115 c.

In the EGR gas cooler 100A, the bypass tubes 110A are provided to allowthe part of the exhaust gas to flow therein. On the other hand, sincethe cooling water is not introduced into the bypass tubes 110A, heatexchange with the cooling water is reduced in the bypass tubes 110A.

For example, a valve device is provided in the first gas tank 151 tocontrol the volume of the exhaust gas to be introduced into the bypasstubes 110A. The valve device can be controlled to permit the exhaust gasto both of the tubes 110 and the bypass tubes 110A or only to the tubes110. Because the volume ratio of the exhaust gas into the tubes 110 tothe exhaust gas into the bypass tubes 110A can be controlled, atemperature of the exhaust gas is controlled.

Since the thermal insulation space 115 c is provided between the firstend bypass tube 110A1 and the partition wall 160, heat exchange betweenthe exhaust gas flowing in the first end bypass tube 110A1 and thecooling water flowing in the end water passage 115 b is reduced. On theother hand, since the end water passage 115 b is provided between thepartition wall 160 and the end tube 110 s, cooling effect of the exhaustgas in the end tube 110 s improves. Accordingly, heat exchangeefficiency improves.

In the second embodiment, the bypass tubes 110A only have theprojections 112 for providing thermal insulation spaces 115 c. That is,the recesses 113 are not formed on the bypass tubes 110A. However, thebypass tubes 110A may have the recesses 113. Namely, the bypass tubes110A can be constructed by using the tubes 110.

In the above description, the ERG gas cooler 100A has two bypass tubes110A. However, the number of the bypass tubes 110A is not particularlylimited to two. The number of the bypass tubes 110A can be changed inaccordance with the required degree of change of the exhaust gastemperature.

Also, the reinforcement plates are provided and joined in the bypasstubes 110A. Instead of the reinforcement plates, recesses recessed fromthe tube main walls 111 toward the inside of the bypass tubes 110A canbe formed, and the recesses of the opposed tube main walls are joined toeach other inside of the bypass tubes 110A.

Other Embodiments

The shape and/or dimension of the recesses 113 can be modified. In theabove embodiments, the dimension of the recesses 113 is equal to theheight of the projections 112. However, the dimension of the recesses113 may reduced depending on resistance of the cooling water to passthrough the inlet openings 113 a, 113 c and the outlet openings 113 b,113 c. Alternatively, the dimension of the recesses 113 may be largerthan the height of the projections 112.

The positions of the recesses 113 can be modified. Instead of thediagonal positions, the recesses 113 may be formed on the samelongitudinal side of the tubes 110. In this case, the water inlet pipe141 and the water outlet pipe 142 are coupled to the same side of thestack of the tubes 110. Therefore, it is not necessary that the watertank 130 is constructed of two tank members 130 a, 130 b. Namely, thewater tank 130 can be constructed of a single tank member.

In the above embodiments, the second raised portions 117 are formedparallel to the short side of the tubes 110. However, the second raisedportions 117 may be modified in accordance with flow conditions of thecooling water. For example, the second raised portion 117 can beinclined relative to the short side of the tube 110 such that a distancebetween the longitudinal end of the tube 110 and the second raisedportion 117 gradually increases with a distance from the inlet opening113 a. Alternatively, the second raised portion 117 may have a curvedshape. Further, each of the flow-adjusting portion may be provided by aplurality of second raised portion 117. That is, the second raisedportion 117 may be divided into plural portions. Furthermore, the secondraised portions 117 may be eliminated.

Further, it is not always necessary that each tube 110 is constructed ofthe first and second tube plates 110 a, 110 b. For example, the tube 110can be formed by a single pipe member.

In the above embodiments, the projections 112 are formed on both tubemain walls 111 of each tube 110, 110A. However, the projections 112 maybe formed on only one of the tube main walls of the tube 110, 110A. Inthis case, the tubes 110, 110A may be stacked such that the tube mainwall 111 on which the projection 112 is formed is opposed to the tubemain wall 111 of the adjacent tube 110, 110A on which the projection 112is not formed. Also in this case, the spaces are provided between theadjacent tubes 110, 110A.

Also, the inner fins 120 may be eliminated in accordance with requiredheat exchange efficiency. Further, one of or both of the outer walls 131of the water tank 130 may be eliminated in accordance with the requiredheat exchange efficiency of the exhaust gas.

Also, it is not always necessary that the water tank 130 has the bulges133. For example, the pipe hole 134 can be enlarged over an area wherethe inlet openings 113 a or the outlet openings 113 b are formed, and abore size of the end of the pipes 141, 142 can be increased so as tocorrespond to the size of the pipe hole 134. In this case, the bulge 133can be eliminated. Thus, the end of the pipe 141 a corresponds to thedistributing portion of the inlet part and the end of the pipe 142corresponds to the collecting portion of the outlet part.

Further, use of the present invention is not limited to the EGR gascooler, but can be employed to any other heat exchangers. For example,the heat exchanger 100 can be used as an exhaust gas recovery heatexchanger that performs heat exchange between the exhaust gas, which isdischarged to air, and the cooling water, thereby to heat the coolingwater.

Also, the material of the components of the heat exchanger is notlimited to stainless steel. The components can be made of othermaterials such as aluminum alloy, or copper alloy depending onconditions in use.

The example embodiments of the present invention are described above.However, the present invention is not limited to the above exampleembodiments, but may be implemented in other ways without departing fromthe spirit of the invention.

1. A heat exchanger for performing heat exchange between a first fluidand a second fluid, comprising: a plurality of tubes, each of the tubesdefining a first fluid passage therein through which the first fluidflows and having a first main wall and a second main wall, wherein atleast one of the first main wall and the second main wall has aprojection along its peripheral end, a first recess and a second recess,the projection projects outside of the tube, the first and secondrecesses are recessed from an end of the projection at predeterminedpositions, wherein the tubes are stacked such that the first main wallsand the second main walls are opposed to each other, second fluidpassages through which the second fluid flows are defined by spacesprovided between opposed first and second main walls of the adjacenttubes and surrounded by the projections, first openings communicatingwith the second fluid passages are defined by the first recesses, andsecond openings communicating with the second fluid passages are definedby the second recesses; a second fluid inlet part disposed incommunication with the first openings for introducing the second fluidinto the second fluid passages; and a second fluid outlet part disposedin communication with the second openings for discharging the secondfluid from the second fluid passages.
 2. The heat exchanger according toclaim 1, wherein the second fluid inlet part includes an inlet portionfor introducing the second fluid and a distributing portion disposeddownstream of the inlet portion with respect to a flow of the secondfluid for distributing the second fluid flowing from the inlet portioninto the second fluid passages, and the second fluid outlet partincludes a collecting portion for collecting the second fluid havingpassed through the second fluid passages therein and an outlet portionfor discharging the second fluid from the collecting portion.
 3. Theheat exchanger according to claim 1, wherein both of the first andsecond main walls have the projections, the first recess and the secondrecess, and the tubes are stacked such that the projections of theadjacent two tubes are opposed to and in contact with each other, thefirst recesses of the adjacent two tubes are opposed to each other todefine the first opening and the second recesses of the adjacent twotubes are opposed to each other to define the second opening.
 4. Theheat exchanger according to claim 1, wherein each of the first andsecond recesses has a dimension equal to a dimension of the projectionwith respect to a direction perpendicular to the first and second mainwalls.
 5. The heat exchanger according to claim 1, wherein the first andsecond main walls have a substantially rectangular shape, and the firstand second recesses are located along longitudinal sides of therectangular shape and on diagonal positions.
 6. The heat exchangeraccording to claim 1, wherein each of the tubes has a flow-adjustingportion on at least one of the first main wall and the second main wallat a position corresponding to an upstream location respect to a flow ofthe first fluid flowing in the first fluid passage, and theflow-adjusting portion is configured such that the second fluid isspread throughout the second fluid passage.
 7. The heat exchangeraccording to claim 1, wherein each of the tubes is constructed of afirst tube member and a second tube member, and the first main wall andthe second main wall are included in the first and second tube members,respectively.
 8. The heat exchanger according to claim 1, wherein eachof the tubes has an inner fin in the first fluid passage.
 9. The heatexchanger according to claim 2, further comprising: a side wall memberattached to longitudinal sides of the plurality of tubes, wherein theside wall member has a bulge at a position corresponding to the firstopenings, the bulge provides a clearance therein and encases the firstopenings, the distributing portion is defined by the bulge, and theinlet portion has a pipe shape and is in communication with theclearance provided by the bulge.
 10. The heat exchanger according toclaim 2, further comprising: a side wall member attached to longitudinalsides of the plurality of tubes, wherein the side wall member has abulge at a position corresponding to the second openings, the bulgeprovides a clearance therein and encases the second openings, thecollecting portion is defined by the bulge, and the outlet portion has apipe shape and is in communication with the clearance provided by thebulge.
 11. The heat exchanger according to claim 9, wherein theplurality of tubes includes an outermost tube stacked at an outermostside, the outermost tube provides an outermost tube wall, the outermosttube wall has an end projection along its peripheral end, a first endrecess and a second end recess recessed from an end of the endprojection, the heat exchanger further comprising: an outer wall memberdisposed along the outermost tube wall such that an end passage isdefined by a space provided between the outer wall member and theoutermost tube wall and surrounded by the end projection, wherein theend passage is in communication with the second fluid inlet part and thesecond fluid outlet part through the first end recess and the second endrecess, respectively.
 12. The heat exchanger according to claim 11,further comprising: a tank having a connecting wall and outer wallsextending from opposite sides of the connecting wall, wherein the tankis coupled to the plurality of tubes such that the outer walls aredisposed along outermost tubes that are stacked at outermost sides,wherein the outer wall member is included in at least one of the outerwalls of the tank, and the side wall member is included in theconnecting wall of the tank.
 13. The heat exchanger according to claim12, wherein the bulge extends over the outer walls of the tank.
 14. Theheat exchanger according to claim 1, further comprising: at least onebypass tube defining a first fluid passage therein through which thefirst fluid flows and a thermal insulation area on its outer periphery,the bypass tube disposed in parallel to the plurality of tubes; and apartition wall disposed between the tubes and the bypass tube toseparate the thermal insulation area from an area where the second fluidflows.
 15. The heat exchanger according to claim 14, wherein the bypasstube has a main wall opposed to the partition wall, the main wall of thebypass tube has a projection that projects toward the partition wall onits peripheral end and contacts the partition wall such that at least apart of the thermal insulation area is defined by a space providedbetween the main wall of the bypass tube and the partition wall andsurrounded by the projection of the bypass tube.
 16. The heat exchangeraccording to claim 14, wherein one of the plurality of tubes, which isopposed to the partition wall, provides an opposed main wall opposed tothe partition wall, the opposed main wall has the projection, the firstrecess and the second recess, the projection projects toward thepartition wall and is in contact with the partition wall such that aspace is provided between the opposed main wall of the tube and thepartition wall and surrounded by the projection of the tube, and thespace is in communication with the second fluid inlet part and thesecond fluid outlet part through the first recess and the second recessof the opposed main wall, respectively.
 17. The heat exchanger accordingto claim 1, further comprising: a first fluid inlet tank defining afirst tank space and having an opening, the first fluid inlet tankcoupled to the tubes such that first ends of the tubes are disposed inthe opening of the first fluid inlet tank and the first tank space isdirectly in communication with the first fluid passages defined insideof the tubes, a first fluid outlet tank defining a second tank space andhaving an opening, the first fluid outlet tank coupled to the tubes suchthat second ends of the tubes are disposed in the opening of the firstfluid outlet tank and the second tank space is directly in communicationwith the first fluid passages defined inside of the tubes.